1. Field of the Invention
The present invention relates to lubrication systems for small internal combustion engines of the type used with lawnmowers, lawn and garden tractors, other small implements, or sport vehicles.
2. Description of the Related Art
Small internal combustion engines typically include a crankcase with an oil sump containing an amount of oil which is conveyed to various lubrication points within the engine to lubricate the moving parts within the engine.
One known lubrication arrangement employs an oil dipper or slinger which is mounted to the end of the connecting rod or to the engine crankshaft which, during the rapid rotation of the engine crankshaft during running of the engine, contacts the oil in the oil sump to agitate and splash the oil into a mist within the engine crankcase. The oil mist contacts and lubricates the various moving parts within the crankcase. Additionally, pressure pulses within the crankcase which are created by the reciprocation of one or more of the engine pistons may be employed to convey the oil mist from the crankcase to other portions of the engine which include moving parts, such as the cylinder head. The foregoing lubrication arrangement is typically referred to as xe2x80x9csplash lubricationxe2x80x9d, and usually is most useful in small, single cylinder engines.
A disadvantage of splash lubrication is that same does not provide pressurized, liquid oil directly to the various lubrication points within the engine, such as shaft bearings. Additionally, splash lubrication systems can be difficult to design which are effective for use in twin cylinder engines and for some vertical crankshaft engines.
In another lubrication arrangement, a gerotor pump, or another suitable type of oil pump, is driven from the crankshaft or camshaft within the engine crankcase. The oil pump is operable to draw oil from the oil sump and force the oil under pressure through passages within the crankshaft and/or camshaft or other oil galleries in the engine housing in order to convey the oil to specific lubrication points within the engine, such as shaft bearings or contact points within the valve train.
A disadvantage with existing lubrications systems which include gerotor or other types of oil pumps is that same typically include a number of moving parts, may be difficult to manufacture, and may require the machining of numerous oil passages in the engine shafts and/or engine housing to convey the pressurized oil to the various lubrication points.
In another arrangement, often referring to as xe2x80x9cdry sumpxe2x80x9d lubrication, the crankcase includes a minimal amount of oil, wherein most of the engine oil is stored in an oil reservoir which is separate from the crankcase. A lubrication pump is driven by the engine, and pumps oil from the oil reservoir through passages in the crankshaft and/or camshaft or other galleries in the engine housing to lubricate the moving parts of the engine. Thereafter, the oil drips back into the crankcase. A scavenge pump, also driven by the engine, pumps the oil within the crankcase back into the oil reservoir.
A disadvantage with dry sump lubrication systems is that same require two oil pumps and a separate oil reservoir, which increases the cost and complexity of such systems.
Additionally, other lubrication systems for small internal combustion engines may include various combinations of some or all of the components of the foregoing lubrication arrangements.
What is needed is a lubrication system for small internal combustion engines which is an improvement over the foregoing.
The present invention provides a lubrication system for small internal combustion engines. In a first aspect of the present invention, a helical oil pump includes a helical insert disposed within a bore in the engine camshaft. The camshaft is rotatably driven from the crankshaft, while the helical insert is rotationally fixed with respect to the crankcase. The lower ends of the camshaft and the helical insert are in communication with the oil sump of the crankcase and, during running of the engine, rotation of the camshaft draws oil from the oil sump upwardly through the bore in the camshaft and around the helical insert to provide lubrication oil directly to the upper camshaft bearing and thence to the upper crankshaft bearing through a passage in the crankcase.
In another aspect of the present invention, an impeller oil pump includes a pump chamber defined between the camshaft gear and a pump body which is rotationally fixed with respect to the crankcase and in communication with the oil sump. An impeller assembly mounted on the camshaft is disposed within the pump chamber such that, upon rotation of the camshaft, the impeller assembly draws oil from the oil sump into the pump chamber. The oil is forced outwardly of the pump chamber through an opening in the camshaft gear in the form of a stream of pressurized oil which is directed toward different locations within the crankcase as the camshaft gear rotates with the camshaft.
Advantageously, the helical oil pump of the present lubrication system provides pressurized lubrication oil directly to the upper camshaft bearing and to the upper crankshaft bearing to lubricate same. Additionally, the impeller oil pump supplies a stream of pressurized oil which is directed toward a plurality of locations within the crankcase as the cam gear rotates, thereby lubricating the crank pin, drive train components, and other moving parts within the crankcase with a stream of pressurized oil. Further, the oil pump is effective to circulate a large volume of oil continuously within the crankcase, such that the stream of pressurized oil which contacts the crankcase walls helps to cool the crankcase and reduce the operating temperature of the engine.
In one form thereof, the present invention provides an internal combustion engine, including a crankcase containing an oil sump therein; a crankshaft rotatably supported within the crankcase; a second shaft rotatably supported within the crankcase in timed driven relationship with the crankshaft, the second shaft disposed vertically and including a bore therethrough which communicates between upper and lower ends of the second shaft; and a helical insert disposed within the bore, the helical insert rotationally fixed with respect to the crankcase, the lower end of the second shaft and the helical insert in communication with the oil sump wherein rotation of the second shaft about the helical insert draws oil from the oil sump upwardly through the bore.
In another form thereof, the present invention provides an internal combustion engine, including a crankcase containing an oil sump therein; a shaft rotatably supported within the crankcase; a plate mounted on the shaft and rotatable therewith, the plate having at least one opening therethrough; a pump body fixed with respect to the crankcase and in fluid communication with the oil sump, the pump body and the plate defining a pump chamber therebetween; and an pump assembly disposed within the pump chamber and mounted on the shaft for rotation therewith; whereby rotation of the shaft and the pump assembly draws oil from the oil sump into the pump chamber and forces oil outwardly of the pump chamber through the opening in the plate.
In a further form thereof, the present invention provides an internal combustion engine, including a crankcase containing an oil sump therein; a shaft rotatably supported within the crankcase, the shaft including a bore therethrough which communicates between upper and lower ends of the shaft; a helical insert disposed within the bore, the helical insert rotationally fixed with respect to the crankcase, the lower end of the second shaft and the helical insert in communication with the oil sump; a plate mounted on the shaft and rotatable therewith, the plate having at least one opening therethrough; a pump body fixed with respect to the crankcase and in fluid communication with the oil sump, the pump body and the plate defining a pump chamber therebetween; and a pump assembly disposed within the pump chamber and mounted on the shaft for rotation therewith; whereby rotation of the shaft and the pump assembly about the helical insert draws oil from the oil sump upwardly through the bore, and draws oil from the oil sump into the pump chamber and forces oil outwardly of the pump chamber through the opening in the plate.
In a further form thereof, the present invention provides a method of cooling an internal combustion engine, including the steps of rotating a shaft within the engine crankcase which includes a plate and an impeller mounted thereon, the impeller disposed within a pump housing at least partially defined by the plate; drawing oil from an oil sump within the engine crankcase into the pump housing through an inlet opening submerged within the oil sump; pressurizing the oil within the pump housing; directing the oil outwardly of the pump housing through at least one opening in the plate, in the form of a pressurized oil stream which rotates with the plate to contact a plurality of locations within the crankcase; transferring heat from the crankcase to the oil upon contact of the stream with the plurality of locations within the crankcase; and allowing the oil to drain from the plurality of locations within the crankcase into the oil sump.